Join Susan as she obsesses about cosmetic chemistry and other things (some possibly related to monkeys). Often strange, occasionally useful, and always worth a stop as a point of interest on your journey through the Intertron.

Tuesday, October 11, 2011

Creating products: Combining the two phases!

After heating and holding, should we add the water phase to the oil phase or the oil phase to the water phase? My first instinct is to add the oil phase to the water phase as, generally, my water phase container is larger than the oil phase container. But then I read something two years ago that encouraged me to add the water phase to the oil phase, some stuff about phase inversion and the like. (Click here for that original revelation!)

But a comment from this post from Anonymous got me thinking yet again! Hi Susan, what I understand from reading the Dr. Z explanation you linked is that the oil phase can be added to the water phase and phase inversion will still occur. Dr. Z described adding the oil phase to the water phase and having an initial w/o emulsion form because of the lack of H-bonding and low HLB of the heated emulsifier. It then said that at the Phase Inversion Temperature the emulsion changes to o/w. It did not mention anything about adding the oil to the water or the water to the oil and any effect of either on phase inversion occurring so I don't understand why you say the water phase must be added to the oil phase.

Great question! So I went off to find stuff to show this reader why I wrote what I wrote. But I couldn't find anything! Everything I found was silent on the issue, or stated something like "add phase B (oil phase) to phase A (water phase) after heating". Hmm. I checked my textbooks - no luck. I checked a ton of data sheets from various companies - including the data sheet on Polawax - and found nothing indicating we should be adding the water to the oil.

But I know I read it somewhere or at least heard it from a very reputable source, because it would have to be on good authority to get me to change what is a lot easier - pouring the oil into the water, which means I'm only using two containers - to something more annoying that required further cleaning! I was about to give up for the day, when I thought I'd check the Dish forum for posts that happened around the day I wrote this post because obviously I had seen something interesting there from Liz. I followed the trail and found this from the mighty LabRat...(I really hope it's okay to post this from the forum because I think it's such valuable information!)

What are the adverse effects if any of mixing the water into the oil?

I suppose technically, adding water to the oil could make a better emulsion. When you add the first few drops of your water phase to the oil phase, you are forming a water-in-oil (W/O) emulsion. As you add more water, your emulsion changes from a water-in-oil (W/O) emulsion to an oil-in-water (O/W) emulsion. This is called a phase inversion. Emulsions that go through a phase inversion are supposed to be better emulsions. This has been supported in the technical literature,

Most cosmetic emulsions are O/W emulsions. There is more water than oil in the formula. It's easier to add a small amount of oil to a large amount of water. When large batches are being made, due to the physical configurations of the main mixing vessel and the stirrer, most often, the stirrer does not reach down far enough to stir the oils as the water is being added.

And these are Liz's comments from the thread that started my brain working!

In an O/W emulsion you add the oil phase to the water phase. For a W/O emulsion you add the water phase to the oil phase. That is because the emulsifiers for each type O/W or W/O is designed to make that particular type of emulsion. Phase Inversion as it is called is reversing these phases which can result in a more stable or unstable product. These methods usually use PIT ( Phase Inversion Temperatures) along with certain types of emulsifers that would offer more stability. I have done it with success a few times. Many other times I ended up with messy separated emulsions.

Very true as well as the addition rate (how fast or slow) will influence the phase to volume ratio for "catastrophic" inversion to take place. Non-ionic O/W emulsifiers typically will go through phase inversion as heating occurs anyway and then settle to the most stable morphology. I think this is what people experience with their varied methods here. Lab Rat mentions heating to the same temp kills bugs but it also will allow for phase inversion to take place or not depending again on temperature, surfactants used, which phase is added first, how much and at what rate (how fast etc.) cooling temp and rate, shear etc.. However this is not to say inversion always takes place to produce a more stable emulsion. Many things can influence stability of emulsions, not just phase to volume ratios. The problem with "catastrophic" inversion and why I personally don't do this method more often is you really don't know the precise time of inversion nor the actual physical conditions you end up with. So I follow the more conventional methods for now.

Uncontrolled phase inversion is typically what we do and it is a hit or miss for stability. The plus to a controlled and hopefully in our uncontrolled phase inversion the end result is a finer and more stable emulsion. At least this has been my understanding how it should be. Ideally in making any emulsions you want to use the least amount of time, energy and emulsifier to produce the best possible emulsion.

So the gist of it all is this: Although adding water to the oil phase can result in a more stable emulsion (and is backed up by science), for us as homecrafters, we seem to have just as much of a chance of messing it up as getting it right because we really don't know when that phase inversion might happen. As both Liz and LabRat are suggesting that the homecrafter should be adding the oil phase to the water phase, I am going to go with this suggestion from now on!

We can add the oil phase to the water phase when making a lotion and still get a great lotion.

Thank you to Anonymous for posing these questions! You've really made me think and change my mind on the topic. I will be updating the various posts on water into oil or oil into water over the next few days!

I really credit the way Anonymous wrote the comments above. Here are a few thoughts I had yesterday on how to approach someone - specifically me - with contradictory evidence. It was done in a curious and respectful way, as one seeker of knowledge to another, with no insults or personal attacks. I really appreciate that approach!

19 comments:

Hm.. I have a problem. I tried to pour the oil phase into the water phase, but there are residues left behind on my beaker - oils plus ewax that are starting to solidify as I pour them into the water. I will have less oils in the oil phase in the final product, and this is not something I would like. I know, I know, the loss is not so important, but it is there.

also, it seemed more reasonable to pour the water, as I have almost zero water loss.

After reading your post, I understand that I may or may not have a lotion that seized no matter in which way I pour the phases.

This males me think :). It would be the second time I am changing a paradigm here - after keeping the two phases in the same beaker and letting them heat simultaneously until they reach 70-75 degrees celsius, and pouring water into oil phase ...

Is there a trick to pouring the oil phase into the water phase WITHOUT any loss?

which makes me go to another question (not really related but ...):

is there a post on the blog where you make any suggestions regarding the mechanical emulsification? What I mean: for how long do we keep mixing in order to make sure that there is an emulsion? I have a blender that goes to quite a high speed, and I mix in 30 seconds bursts with a short break , up to 3-4 minutes. Then I leave the lotion sit until it cools down to the temp where I can add the preservative and other heat sensitive ingredients, then mix again in 30 second bursts, for 3-4 minutes. For me it seems to be enough. But is it really?

I have always opted to pour the water into the oil because it's so hard to get all of the oil phase out of the container and into the water. Plus by dumping the water quickly, I like to think that it helps with the emulsification?

For example, I have reviewed several prototype cream and lotion formulations published by Croda with Polawax being used as the primary emulsifier. In all the formulations the polawax was melted with the oil phase. Some of the procedures had the water phase being added to the oil phase and other procedures had the opposite.

For some emulsifiers it may make a difference but for others probably not.

Before using an emulsifier we would always review prototype formulations with the suggested procedure by the ingredient manufacturer. Unfortunately, hobbyists do not always have the same access to prototype formulations as do commercial cosmetic labs.

In any case, to maintain a consistent product once you have found a method that works it is important to stick to the same procedure. This is called a standard operating procedure which records such data as mixing equipment, mixing speed, temperature, rate of cooling, order of mixing ingredients etc.

Cosmetic formulation is partly science and partly art. As such, there is no one right way and a lot of experimentation is required to achieve your desired result.

Hi Sarah, I am SO glad she asked you because I was having a hard time understanding all the science... thanks for responding in a nice post where we can all see and take the journey with you both.

I have been making creams both ways... I haven't personally seen a difference in stability (yet) but at least I know that using the (oil into water) method shouldn't be to my detriment.

@Nedeia - I had that solidification issue just once, I think it was because the sides of the beaker were cooling much faster than the bottom and therefore cooling the oils on the way out so I switched to using a stainless steel bowl shaped container which seemed to work (otherwise I guess you'd have to try pouring faster :) )

As for the mechanical process - I was taught to whisk/mix/blend continuously for at least 5 mins before the first rest interval/break and then go again for say a minute then break and so on for about 10 mins; but I also know some who blend almost continuously for 20 mins! I'd love to hear what other people do. What are your thoughts Sarah?

I am totally still a newbie, but I find that I put my water phase into my oil phase, as others have said I think its easier to pour water out than to pour oil out. So far my very few lotions have been a success.

I just wanted to point out that in the Polawax doc linked above, it says "Once the two phases reach this temperature, the water phase is added to the oil phase in a thin stream using mechanical agitation." under the "Usage" section.

If you have an ingredient that you need to add at high quantities, like 10%-15%, but it needs to be added in the cool down phase, how can you do that? I'm thinking that adding 15% of an ingredient in the cool down phase will destabilize the emulsion, would it not? If you get both phases at 40°C, add the ingredient, then combine the phases, that wouldn't work either, since the droplet size would have grown too much at that temperature, correct? If so, then how can you add a heat sensitive ingredient at 15% in a formula?

What ingredient do you want to use, Li Xua. If I knew this, along with your recipe in percentages, I'd be able to answer better. It may be that the ingredient you want to use can be added at higher temperatures or you're using too much or something else. As well, 40˚C - I prefer 45 ˚C for my cooling phase - isn't a low temperature, so things are still emulsifying well then, depending upon whether you heated and held and your emulsifier and so on. So I guess I come back to asking you to share your recipe in percentages so I can help better.

I came accross a few such ingredients that require a pretty large minimum quantity, yet they are heat sensitive (most explicitly say in the description that they are not to be used above 40˚C). For example, AHA Fruit Acids from Making Cosmetics seems to require a minimum of 5% and can get up to 15%, but should not be added at >40°C. If I add 5% of this and 2% panthenol in the cool down phase, then I don't have much room for anything else. I am quite puzzled as to how I would be able to incorporate, say, 10% of this ingredient in a cream.

There are also ingredients that are dissolved for easier use, such as a willow bark extract solution (INCI: water and willow bark extract) that's standardized at 10% BHA (so I would need to add 10% of the solution in order to get 1% BHA in the final cream), but again, it's heat sensitive.

This is a cream that I'd like to add the 10% willow bark extract solution to:

I noticed now in the Argireline NP sample recipe at Making Cosmetics that they have a cool down phase totalling 10.5%. I'm also noticing that they're using a gelling emulsifier (so would that mean that this last 10.5% phase is actually mixed in with the gel formed by this polymer, instead of being emulsified? it would be great if this wasn't the only solution to the problem)

Hi Li! My suggestion is to make a small batch of this product and see how much cool down phase it can take. There isn't a set amount for cool down phase, like 10%. I've made products with much higher cool down phases and they work well. I think trying this recipe in a small amount - 100 grams, say - is the best way to go. This seems like it'll be a really hydrating and protecting product, but you might want to check the viscosity of it when it only has 60-ish% water phase.

I guess the bigger question is why do you need so many things in one product? Do they go well together or could you make another product with some of the ingredients in there, like a toner or facial wash?

And I wouldn't suggest 1% allantoin. 0.5% is very effective and won't cause shards like 1% will do. Let us know how this turns out!

I want to make a cream for sensitive oily skin with seborrheic dermatitis that's emollient, hydrating and anti-inflammatory. After some tweaking I arrived at this formula. I've been using it for a few months now and I'm actually really happy with it so far (the consistency is more like a lotion than a cream - will thicken it a bit more). I also don't think I noticed any issue with the allantoin yet. What should be happening with it at 1%?

The reason I want to add BHA is that I also want it to be effective against acne, and unfortunately the only BHA product I have access to at the moment is this solution that needs to be added at 10% for 1% BHA (although I'll probably just use 0.5% BHA).

I did consider making more products, each doing less things, but in the end I didn't see much advantage to that. The ingredients do seem to work very nicely together (I'm not aware of any incompatibility between them) and I end up with a single product that I can apply easily. I am a bit concerned about the niacinamide + acid combination, will need to see how that turns out (this could be a case where they just don't go very well together and I'll need to make a separate product).

I made a cream with almost 9% cool down phase and it seems to work nicely so far! (68.75% water and 31.25% oil, out of which 6.7% emulsifiers) Thanks for encouraging me to try! (I can only conduct very few experiments unfortunately, which is why I was so reluctant to try something that I thought would have a high chance of destabilizing the emulsion)

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I'm an aspiring cosmetic scientician and DIY girl interested in pretty much any craft you can name - bookbinding, jewellery making, sewing, paper crafts, polymer clay - but my main passion is bath & body product making.
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